# 死信隊列 死信交換機（Dead-Letter-Exchange），當消息在一個隊列中變成死信之后，它能被發送到另一個交換機中，這個交換機就是DLX，綁定DLX的隊列就稱之為死信隊列 消息變成死信一般是由于下面三種情況： * 消息被拒絕（Basic.Reject或Basic.Nack），并在調用時設置requeue參數為false * 消息過期 * 隊列達到最大長度通過在channel.queueDeclare方法中設置x-dead-letter-exchange參數來為這個隊列添加DLX ``` $connection = new AMQPStreamConnection('127.0.0.1', 5672, 'why', 'why'); $channel = $connection->channel(); //測試死信的上游交換機 $channel->exchange_declare('dlxBeforeExchange', 'direct', false, true, false, false, false, []); //死信的交換機 $channel->exchange_declare('dlxExchange', 'direct', false, true, false, false, false, []); //測試死信隊列的上游隊列 $dlx_table = new \PhpAmqpLib\Wire\AMQPTable(); $dlx_table->set('x-dead-letter-exchange', 'dlxExchange' ); $dlx_table->set('x-dead-letter-routing-key', 'dlxKey' ); $channel->queue_declare('dlxBeforeQueue', false, true, false, false, false, $dlx_table); $channel->queue_bind('dlxBeforeQueue', 'dlxBeforeExchange', 'dlxBeforeKey'); //死信隊列 $channel->queue_declare('dlxQueue', false, true, false, false, false); $channel->queue_bind('dlxQueue', 'dlxExchange', 'dlxKey'); $head = array_merge(array('content_type' => 'text/plain', 'delivery_mode' => AMQPMessage::DELIVERY_MODE_PERSISTENT), ['expiration' => '60000']); $msg = new AMQPMessage('hello why', $head); $res = $channel->basic_publish($msg, 'dlxBeforeExchange', 'dlxBeforeKey'); ```